International patent application number PCT/AU99/00949, in respect of which the present assignee is a licensee, discloses a method and apparatus for imaging an article and in particular for determining the phase of a radiation wave field which passes through the article. This invention has particular application to providing internal structural details and thickness information relating to substantially transparent objects which cannot be easily inspected using normal intensity imaging of the object.
In order to provide the phase determination the above International application provides a solution to the transport of intensity equation.
In order to solve the above-mentioned equation images of an object are taken at different planes within the depth of field of the optics used to capture the images and that data is processed to provide the required phase information. Whilst the above International application provides extremely good results in terms of the imaging and thickness of the object it does not provide significant information relating to the surface profile of the object or, in other words, the manner in which the surface of the object changes with respect to a predetermined datum such as a plane passing through the object.